The use of azole antifungals, including fluconazole, for treatment and/or prophylaxis against infections caused by Candida albicans has resulted in a recent, dramatic increase in Candida strains that are resistant to antifungal drugs. This is true in oral candidiasis in AIDS patients, and has recently been documented in other immune compromised individuals including blood and marrow transplant recipients (BMT). In the past several years, the basic molecular mechanisms of azole resistance have been identified including the overexpression of the target enzyme and two types of efflux pump, and mutation in the target enzyme. Recent data from this laboratory and others has indicated that resistance is a whole cell response in which virulence determinants can have an effect on resistance, and resistance determinants can have an effect on these other virulence factors. This whole cell response includes a heterogeneous resistance (Het-R) phenotype identified in our laboratory, in which certain susceptible isolates are able to form small colonies on agar plates containing fluconazole. This Het-R phenotype may be correlated with the ability to induce true resistance in these strains, and is related to heterogeneous resistance in bacteria. The overall goal of this project is to develop an understanding of the whole cell response of C. albicans to azole antiflingals, including the Het-R phenotype. The specific aims of this proposal are: 1) to characterize the interactions between resistance and virulence factors of C. albicans, 2) to characterize the transcriptional regulation associated with the whole cell response, and 3) to characterize this Het-R phenotype as a specific whole cell response. Antifungal drug resistance and susceptibility testing has become increasingly important as invasive candidiasis has become a leading cause of nosocomial infections worldwide. The analyses outlined in this proposal will define some of the many responses of a cell to azole antifungal drugs, thus providing us with information critical to the development of effective strategies to prevent, diagnose or treat fungal infections.